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What are some differences between aerobic respiration and fermentation?

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Aerobic respiration and fermentation both enable cells to release energy from glucose, but the specific start-to-finish pathway by which this is accomplished is one of the main differences between the two processes. Aerobic respiration requires oxygen and fermentation does not. The structures within a cell that are called mitochondria are responsible for the significant portion of aerobic respiration, while fermentation is carried out in the fluid portion of a cell's cytoplasm.

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Both aerobic respiration and fermentation begin with the metabolic pathway called glycosis, which transforms glucose into pyruvate, or pyruvic acid. The pathway toward energy-release changes at this point, depending upon the metabolic process. In aerobic respiration, pyruvate next enters the tricarboxylic acid cycle, also known as the TCA cycle or Krebs cycle, where it is oxidized to release carbon dioxide and ultimately reduced to the coenzyme called NADH. The next step of aerobic respiration pushes the NADH along the electron transport chain to become the final end product adenosine triphosphate, or ATP, the energy-currency unit that the cell requires to fuel its metabolism.

Fermentation sends pyruvate along a different pathway in which it is not transferred to the cell's mitochondria, but remains within the cell's cytoplasm instead. Depending upon whether the process is taking place within an animal or a plant cell, fermentation ultimately produces either lactate or ethanol respectively. Both end products are stored for energy-release use when needed. As in aerobic respiration, ATP is the agent produced to transport energy throughout the cell.

Fermentation is the less-efficient process and produces only two molecules of ATP from each molecule of glucose, but it is the much faster energy-release process. It can also be used when oxygen levels have been depleted and the cell requires a quick burst of energy.

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